Design and characterisation of bodipy sensitizers for dye-sensitized NiO solar cells

Abstract

A series of photosensitizers for NiO-based dye-sensitized solar cells is presented. Three model compounds containing a triphenylamine donor appended to a boron dipyrromethene (bodipy) chromophore have been successfully prepared and characterised using emission spectroscopy, electrochemistry and spectroelectrochemistry, to ultimately direct the design of dyes with more complex structures. Carboxylic acid anchoring groups and thiophene spacers were appended to the model compounds to provide five dyes which were adsorbed onto NiO and integrated into dye-sensitized solar cells. Solar cells incorporating the simple Bodipy-CO₂H dye were surprisingly promising relative to the more complex dye 4. Cell performances were improved with dyes which had increased electronic communication between the donor and acceptor, achieved by incorporating a less hindered bodipy moiety. Further increases in performances were obtained from dyes which contained a thiophene spacer. Thus, the best performance was obtained for 7 which generated a very promising photocurrent density of 5.87 mA cm(-2) and an IPCE of 53%. Spectroelectrochemistry combined with time-resolved transient absorption spectroscopy were used to determine the identity and lifetime of excited state species. Short-lived (ps) transients were recorded for 4, 5 and 7 which are consistent with previous studies. Despite a longer lived (25 ns) charge-separated state for 6/NiO, there was no increase in the photocurrent generated by the corresponding solar cell.

Two‐Photon Absorption Properties and Structures of BODIPY and Its Dyad, Triad and Tetrad

“…Besides that, each BODIPY displays slight changes according to their chemical functionalization. Therefore, Ph 3 N‐BODIPY‐1 features a band located at 300 nm corresponding to the triphenylamine group transitions as reported in the literature before . BODIPY‐2 is the only dye which presents a different profile for its main absorption band, i. e .…”

“…Subsequent oxidation using p ‐chloranil easily lead to form the dipyrrin then further complexation to yield the borondifluoro moiety. The synthesis of Ph‐BODIPY‐1 and Ph 3 N‐BODIPY‐1 were previously described and the BODIPY‐2 was prepared following a modified procedure reported in the literature . The synthesis of BODIPY‐3 and BODIPY‐4 is illustrated in Scheme .…”

“…Ph 3 N‐BODIPY‐1 : The 4‐formyltriphenylamine (100 mg, 0.366 mmol, 1 eq.) and 2,4‐dimethyl‐3‐ethylpyrrole (100 μL, 0.768 mmol, 2.05 eq.)…”

A theoretical and experimental NMR study of BODIPY 493/503: difluoro{2‐[1‐(3,5‐dimethyl‐2H‐pyrrol‐2‐ylidene‐N)ethyl]‐3,5‐dimethyl‐1H‐pyrrolato‐N}boron

“…Compound 1 is bright, green fluorescent dye with similar excitation and emission to fluorescein with several uses in biochemistry, for staining lipids, membranes and other lipophilic compounds, because they exhibit narrow emission bandwidths, they have high extinction coefficient and fluorescence quantum yields and they are photostable. [1] Other applications of these dyes are related to fluorescent probes, [2][3][4] deep-red lighting sources, [5] bioactive CO-releasing molecules [6] and solar cells, [7] amongst many others. [8][9][10] Concerning BODIPY NMR properties, there are several compounds with reported data (Scheme 1) especially related to [11] ; 4, 1 J 11B19F = 33.4 Hz [12] ; 5, 11 B = 0.28, 1 J 11B19F = 28.7 Hz [13] ; 6, 11 B = 0.…”

Designing Squaraines to Control Charge Injection and Recombination Processes in NiO‐based Dye‐Sensitized Solar Cells

“…Current activities in the area of p‐type DSSCs focus on developing novel photosensitizers to improve the general device performance . Here, a number of key requirements need to be met: i) a broad absorption spectrum with a high extinction coefficient should be guaranteed; ii) the highest‐occupied molecular orbital (HOMO) energy of the sensitizer must lie below the valence band (VB) energy of the p‐type semiconductor; iii) the lowest‐unoccupied molecular orbital (LUMO) energy should be placed above the redox potential of the electrolyte to ensure efficient electron injection and regeneration, respectively; iv) a high photo‐ and thermal‐stability is required .…”